Minimally invasive medical procedures generally employ small diameter instruments that can be inserted through a small incision or a natural orifice to reach a work site inside the body of a patient. One type of instrument that is useful for minimally invasive procedures is a bipolar vessel sealer. A bipolar vessel sealer can seal a blood vessel by simultaneously clamping the vessel closed and directing an electrical current through the vessel tissue to cauterize the vessel tissue and thereby seal the vessel. Such vessel sealers generally have jaws that must be able to apply clamping pressure that is sufficient for sealing of the vessel. Another general requirement of a vessel sealer is that the jaws of the vessel sealer be long enough to hold a flattened vessel without the edges of the vessel protruding from the closed jaws. Accordingly, the jaws must be correspondingly longer for sealing larger vessels. Long jaws and high clamping pressures create reaction torques and forces in the structure of the vessel sealer. However, miniaturized instruments used in minimally invasive procedures generally have small components that are actuated using cables that extend along the length of a tube that is inserted in a patient. These components have strength limitations that limit the amount of force and torque that the vessel sealer can deliver.
The clamping pressure applied during vessel sealing is equal to the ratio of the applied force to the area over which the force is applied. Accordingly, the surface areas of the faces of the jaws of a vessel sealer can be reduced to achieve the desired clamping pressure without exceeding the force or torque limitations of the actuation structure. Since the length of the jaw is set by the size of the largest vessel to be sealed, only the width of the jaw can be decreased to reduce the area of the jaw face. However, there are limits in how thin jaws can be made. If the jaws of a vessel sealer are too thin, the jaws will be weak and could deflect or bend under load when sealing a vessel or when being used for purposes such as blunt dissection or grasping. Blunt dissection can use the tip of the vessel sealer to move or separate tissues and may apply forces that the thinnest portions of the jaws must support. Similarly, the vessel sealer could be used as a general grasper and would need the ability to securely grasp both fine and bulk tissue under varying loads. A vessel sealer is thus sought that can apply the clamping pressure required for reliable sealing of vessels without exceeding the strength limitations of the actuating structure while still being able to support working forces during use for vessel sealing or other purposes.